The head of the UN's panel of climate-change experts said on Friday he was encouraged by climate pledges at last week's G8 summit but warned commitments still fell short of what was required by science.
Rajendra Pachauri, chairman of the Nobel-winning Intergovernmental Panel on Climate Change (IPCC), told AFP the outcome of the L'Aquila talks was "a bit of a dichotomy."
"On the one hand, the G8 leaders have agreed to this so-called aspirational goal of reducing (greenhouse-gas) emissions by 80 percent up to 2050, and seeing that temperature increase doesn't exceed two degrees (Celsius)," he said.
"But on the other hand, they haven't take into account the IPCC's assessment that if we want to limit the increase to two degrees, we have to ensure that emissions peak no later than 2015.
"If that's the case, they should have clearly come up with what they are going to do about reducing emissions in the immediate, short run. They haven't done that. I see that as a gap that hasn't been filled."
The UN's 192-nation Framework Convention on Climate Change (UNFCCC) is hosting talks aimed at forging a new global pact for tackling global warming and its impacts.
The treaty would take effect after 2012, ratcheting up curbs on greenhouse-gas pollution set down in the landmark Kyoto Protocol.
But little more than five months are left for wrapping up the process, launched as a "roadmap" in Bali in 2007. A planetary-wide conference in Copenhagen in December will be the climax.
The world's eight top industrialised nations set a goal of at least halving greenhouse gas emissions by 2050, with rich economies curbing their own pollution by 80 percent by this date.
But the aim was not endorsed in the G8's meeting the next day with China, India and Brazil and other emerging giants.
The two summits also supported the aim of limiting warming to two degrees (3.6 degrees Fahrenheit) over pre-industrial levels. The target was sketched by the IPCC in its 2007 Fourth Assessment Report as a means of averting the worst damages of climate change.
Neither summit, though, saw any advance on an emissions target for 2020, which many experts say is more important than a distant objective for mid-century.
Pachauri was interviewed by phone in Venice, where the IPCC met to sketch the parameters of the Fifth Assessment Report, which will be issued in several volumes from 2013.
He fended off criticism that the six-year gap between the fourth and fifth reports was too long.
Some commentators have said climate change is happening faster than thought and the IPCC process is too ponderous. As a result, policymakers are not being kept up to speed with scientific analysis of the threat, according to this view.
"Everything that we said in the Fourth Assessment Report still holds valid," Pachauri contended.
"You've got to take a balanced and comprehensive view of all the literature that comes out. There's always a danger if the IPCC is going to base assessment on just a year or two of observations, or a year or two of research outputs, we could actually be playing into the hands of the (climate) skeptics."